Foams of aromatic polycarbonates and processes for their production are known. For example, aromatic polycarbonates can be foamed with blowing agents which give off nitrogen or carbon dioxide - decomposition blowing agents (cf. DE-AS 1,031,507 and DE-OS 2,434,085). A distinct reduction in molecular weight is generally observed. The non-volatile decomposition products of the blowing agent remain in the foams.
It is also known that aromatic polycarbonates can only be satisfactorily processed if they are completely dry. Any moisture present leads during processing to a reduction in molecular weight and to the formation of bubbles (cf. Plastics Technology 10, 1964, pages 32 to 36; GB-PS 841, 652) .